Electric lamp



May 24, 1938. C. J LE BEL 2,118,452

ELECTRIC LAMP Original Filed Aug. 14, 1929 INVENTQOR CLARENCE J 5551. BrQ Arrow/5r Patented May 24, 1938 PATENT OFFICE- ELECTRIC LAMP ClarenceJ.

Le Bel, New York, N. Y., assignor to Raytheon Manufacturing Company,Newton,

Masa, a corporation of Delaware Original application August 14, 1929,Serial No. 385,707. Divided and this application January 28, 1935,Serial No. 3,689

5 Claims.

This invention relates to electric lamps and particularly to a lampwhich will radiate a substantial portion of its energy in apredetermined portion of the spectrum. The lamp of this invention ischaracterized by an extraordinary high output of energy lying in theultra-violet portion of the spectrum.

A lamp of this character has great utility in many fields. Thus forsterilizing and antiseptic purposes, such a lamp is very eiiicient.Furthermore, many chemical reactions, especially obscure organicreactions such as are involved in the tanning of leather, treating offoods and the like, are greatly accelerated by ultra-violet light. Forpurposes such as these it has been found that only a comparativelynarrow portion of the spectrum in the ultra-violet region is useful, andany of the radiant energy outside of this spectrum is therefore wasted.While devices such as mercury arcs in quartz containers are generatorsof substantially powerful ultra-violet rays, their radiant energy isnevertheless distributed over a considerable spectrum in this regionwith a resultant loss of efiiciency.

An object of this invention is to devise a lamp in which radiant energyin a certain portion of the ultra-violet spectrum is generated in a muchmore efficient manner than has previously been the case. A furtherobject is to devise a lamp which will be simple and cheap.

I have discovered that a metal vaporasuch as mercury, and an inert gas,such as argon or neon, at certain pressures when carrying a discharge,exhibit a remarkable phenomenon. Under operating conditions the pressureof either one of the rare gases may be between 1 and 8 mm. while thepressure of the mercury must be between 1 and 8 microns. The pressure ofthe rare gas is not very critical, and may be varied over substantiallywide limits. It is, however, necessary to maintain the mercury pressurewithin critical limits. This may be done by either having the necessaryamount of cooling surface in the tube or by artificially cooling thetube so that the desired pressure is maintained.

Sodium or other easily vaporizable metals may also be used instead ofmercury, while a comparatively inert gas like nitrogen may be usedinstead of neon. In general the gas should have a high ionizationpotential.

When a lamp with such a mixture of gas is energized so that the gastherein becomes ionized, I have discovered that as much as 65% of thetotal radiant energy is emitted in the form of ultra-violet light havinga wave length'in the case of mercury of about 2537 Angstrom units. Byvarying the pressure of the mercury within narrow limits, thispercentage may be reduced somewhat as the energy goes into other wavelengths. v Apparently some obscure resonance phenomenon is involved inwhich rare gas particles freely interact with mercury particles totransfer substantially all energy to the latter, and cause it to emit asdescribed. It is possible that some unstable compound of mercury andrare gas is formed which emits its characteristic radiation. Theradiation emitted will in general be one of the prominent lines of thesubstance having the lower ionization potential, in this instancemercury.

By varying the mercury pressure over the wider limits, as from 1 to 20microns, it is possible to ionize both the gas and the vapor, and changethe color of the resulting light. In fact it is possible to go from thepure color of the gas to the pure color of mercury through thecombination of the two colors by properly adjusting the mercury vaporpressure. In this latter case, however, the lamp does not emit as greata portion of its energy in the narrow region of the ultra-violetspectrum as is true when the mercury pressure is maintained withinsmaller limits.

Referring to the drawing, the figure shows an induction lamp drawn tofull size.

In the figure is shown in true form, at substantially full size, anelectrodeless induction lamp comprising a tubular portion Hi and bulbH2. Either or both may be made of material transparent to theultra-violet rays generated. A coil H3 energized by a suitable source ofhigh frequency, such as an oscillator H4, encircles bulb H2 andenergizes the lamp.

After the tube has thus been constructed, it is treated in the customarymanner to remove all occluded gases, and exhausted to a high vacuum. Asmall drop of mercury vapor, indicated by M, may be introduced withinthe container. In addition, a quantity of argon or neon may beintroduced so that at the operating temperature of the tube, thepressure will preferably be within the limits previously specified. Whenthe tube is first started, much of the discharge is carried by the raregas. The discharge, however, warms the mercury so that its pressurebecomes sufllcient for it to partake of the discharge. Within a veryshort space of time the lamp begins to function as a generator ofultra-violet rays.

For example, in a lamp embodying my invention and containing neon atabout 4 mm. and mercury at about 2 microns, a discharge resulted in avery powerful emission of ultra-violet in a region of the spectrum below2900 Angstrom units. A major portion of this energy was concentrated inthe 2537 line. During the operation of this lamp, the current andpressure within the lamp could be adjusted so that practically thegreatest portion of the energy was concentrated in the 2537 line.

This application is a division of my co-pending application, Serial No.385,707 filed August 14, 1929.

What is claimed is:

1. As a new and improved article of manufacture, a container, aninduction coil passing around a major portion of the wall of saidcontainer, a medium located within said container and adapted to becomeexcited into luminescence by the passage of an alternating currentthrough said induction coil, so as to produce an arc of predetermineddimensions within said container, a minor portion of the wall of saidcontainer being sufficiently spaced from said arc so that thetemperature of said spaced part of the wall remains sufficiently low toprevent the pressure within said container from exceeding apredetermined. limit.

2. As a new and improved article of manufacture, a container havingtherein a gas and mercury, said container having a spherical portion ofrelatively large volume, and a coil substantially surrounding saidspherical portion so that said spherical portion is directly with thefield of said coil, said spherical portion having an integral extensionwhich is beyond the field of said coil and which has a smaller volumethan said spherical portion.

3. As a new and improved article of manufacture, a container having agas and a vaporizable material located therein, a coil surrounding themajor portion of said container, said coil being adapted, when 'the sameis energized by the passage of an electric current through the same, tovaporize said material and to cause said gas and said vaporized materialto emit light, said container having a minor portion oi. the wallthereof spaced from the zone of direct luminescence.

4. As a new and improved article of manufacture, a container having agas and a vaporizable material located therein, a coil surrounding themajor portion of said container, said coil being adapted, when the sameis energized by the passage of an electric current through the same, tovaporize said material and to cause saidgas and said vaporized materialto emit light, said container having a condensing chamber integraltherewith and sharply defined from that portion of the container whichis surrounded by said coil, said condensing chamber being beyond thezone of direct luminescence.

5. A method of producing light which consists in exciting intoluminescence a gas which is located within an enclosed chamber and alsoexciting into luminescence a vapor which is located within said enclosedchamber, so as to produce a definite zone of direct luminescence, andallowing a part of said container which is beyond said zone to remainrelatively cool in order to form a condensing chamber for said vapor,the volume of said condensing chamber being smaller than the volume ofsaid zone, said gas and vapor being excited into luminescence by anelectro-magnetic field which is produced external to said container.

CLARENCE J. LE BEL.

